1. Field of the Invention
The present invention relates to a lens barrel used in an optical system.
2. Related Background Art
In a small-sized camera having a multi-focal-point lens (zoom lens), the barrel is expanded and contracted to change the distance between an in-barrel lens (lens group) and a focal surface and hence the magnification (hereinafter, also referred to as zooming). At this time, the lenses in the barrel are divided at least into two groups to change the distance between the lens groups to a distance suited for each zoom ratio. Also, the movement of image focusing (hereinafter, also referred to as focusing) is required for any magnification. Focusing is conducted by changing the position of in-barrel lens relative to a focusing plane. Conventionally, as an expansion-and-contraction mechanism for such a lens barrel, it has been a general technique to make the lens barrel in a circular section and employ a helicoid mechanism.
In recent years, down-sizing and high-power zoom-ratio have been advanced for optical apparatuses thus demanding in high-density and high-integration of the parts. Furthermore, there is another demand for cost reduction by reduction in the number of parts or modification to parts easy to manufacture (easy for resin forming, etc.). In particular, this tendency is conspicuous for the small-sized cameras. Under the situation, there is a demand for further improving the expansion and contraction mechanism for a lens barrel stated above. Therefore, it is an object of the present invention to provide a lens barrel having an expansion and contracting mechanism high in space efficiency and excellent in productivity.
According to a first aspect of the present invention, a lens barrel comprises: a first cylinder sliding in an optical axis direction of an optical system, a second cylinder sliding in the optical axis direction while rotating about the optical axis as a rotation axis, a base for accommodating the first cylinder and the second cylinder therein, a single motor as a drive source for sliding both of the first cylinder and the second cylinder, a feed screw being provided in the base to slide the second cylinder due to a drive force of the motor, a rotation mechanism being provided in the base to rotate the second cylinder due to the drive force of the motor, a helicoid mechanism formed in an outer peripheral surface of the first cylinder and an inner surface of the second cylinder, and a drive gear to transmit a drive force of the motor to the feed screw and the rotation mechanism. The drive gear comprises a cylindrical gear and a shaft gear having a shaft inserted in the cylindrical gear. The cylindrical gear and the shaft gear rotate about a common rotation axis. The second cylinder is allowed to protrude from an interior of the base toward a subject, and the first cylinder is allowed to protrude from an interior of the second cylinder toward the subject due to the helicoid mechanism and rotation of the second cylinder. The cylindrical gear is interposed between the rotation mechanism and the motor, and the shaft gear is interposed between the feed screw and the motor.
Preferably, a pair of first and second gears are included. They rotate about a common rotation axis. The first gear is interposed between the shaft gear and the motor, and the second gear is interposed between the cylindrical gear and the motor. Any one of the first gear and the second gear has an elongate hole formed in a circumferential direction and the other has a protrusion protruding into the elongate hole.
More preferably, a first lens group, a second lens group and a cam mechanism are included. The second lens group is movable relative to the first lens group in the first cylinder. The cam mechanism comprises cam pins and cam grooves. The cam pins protrude from a lens holder toward an interior of the second cylinder. The lens holder holds the second lens group. The cam grooves are formed in the inner surface of the second cylinder. The second lens group is moved relative to the first lens group by the cam mechanism and protruding movement of the first cylinder from the second cylinder.
According to a second aspect of the present invention, a lens barrel comprises: a first cylinder sliding in an optical axis direction of an optical system, a second cylinder sliding in the optical axis direction while rotating about the optical axis as a rotation axis, a base for accommodating the first cylinder and the second cylinder therein, a single motor as a drive source for sliding both of the first cylinder and the second cylinder, a feed screw being provided in the base to slide the second cylinder due to a drive force of the motor, a rotation mechanism being provided in the base to rotate the second cylinder due to the drive force of the motor, a cam mechanism comprising pins protruding from the first cylinder and cam grooves formed in the inner surface of said second cylinder, and a drive gear to transmit a drive force of the motor to the feed screw and the rotation mechanism. The drive gear comprises a cylindrical gear and a shaft gear having a shaft inserted in the cylindrical gear, and the cylindrical gear and the shaft gear rotate about a common rotation axis. The second cylinder is allowed to protrude from an interior of the base toward a subject, and the first cylinder is allowed to protrude from an interior of the second cylinder toward the subject due to the cam mechanism and rotation of the second cylinder. The cylindrical gear is interposed between the rotation mechanism and the motor, and the shaft gear is interposed between the feed screw and the motor.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.